Once again I broke a compiler…

Back when I was writing FORTRAN ‘for real’ (a.k.a. in a production environment), I managed to find a bug in the FORTRAN compiler that was confirmed and verified independently by the compiler creator and supplier.

Not that I was too happy about it as the bug was totally reproducible and quite severe. It was also just obscure enough that it was never fixed. We worked around it and then went on to other things.

Well, I’ve found a bug in another compiler. This one dates from the same time frame, but is the Digital Research PL/I compiler I’ve been playing with on my Z80 single board.

Now, disclaimer: this ‘bug’ may well be a known and documented condition, but it’s not in the DR written PL/I compiler manual, and any other documentation has probably been lost over the ages.

So with that, I mentioned in my last post that I had to build my own ‘doexp()’ subroutine for the concentration program because squaring a negative number was failing ‘Error(3)’.

Well, it happened again. This time I was converting an old fracture program from FORTRAN and it was failing with OVERFLOW(1) errors. After some serious tracing with debug prints, I found it was again the ‘**’ exponent function that was the cause. Looking at the numbers coming from the program, there was NO WAY it could be a real calculation problem (-.0152534 ** 2 is NOT an overflow!!!) so it had to be the ‘**’ again.

To verify I grabbed the ‘doexp()’ subrouting from the concentration program and popped into the fracture program, and sure enough it runs.

As there is no way I can examine the source of the built-in function, I’ll just have to use my ‘doexp()’ from now on.

At least the program runs now. 🙂

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